1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction magnetic transducer for writing and a method of manufacturing the thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought with an increase in surface recording density of a hard disk drive. A composite thin-film magnetic head has been widely used which is made of a layered structure including a recording head having an induction magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called and AMR head or simply MR head. A reproducing head using a GMR element is called an GMR head. An AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head whose surface recording density is more than 3 gigabit per square inch.
An AMR head includes an AMR film having the AMR effect. In a GMR head the AMR film is replaced with a GMR film having the GMR effect and the configuration of the GMR head is similar to that of the AMR head. However, the GMR film exhibits a greater change in resistance under a specific external magnetic field compared to the AMR film. As a result, the reproducing output of the GMR head is about three to five times as great as that of the AMR head.
An MR film may be changed in order to improve the performance of a reproducing head. In general, an AMR film is made of a magnetic substance that exhibits the MR effect and has a single-layer structure. In contrast, many of the GMR films have a multilayer structure consisting of a plurality of films. There are several types of mechanisms of producing the GMR effect. The layer structure of a GMR film depends on the mechanism. GMR films include a superlattice GMR film, a granular film, a spin valve film and so on. The spin valve film is the most efficient since the film has a relatively simple structure, exhibits a great change in resistance in a low magnetic field, and is suitable for mass production. The performance of a reproducing head is thus easily improved by replacing an AMR film with a GMR film and the like with an excellent magnetoresistive sensitivity.
Besides selection of a material as described above, the pattern width such as the MR height, in particular, determines the performance of a reproducing head. The MR height is the length (height) between the end of an MR element closer to the air bearing surface and the other end. The MR height is controlled by an amount of lapping when the air bearing surface is processed. The air bearing surface is the surface of a thin-film magnetic head that faces a magnetic recording medium and may be called track surface as well.
Performance improvements in a recording head have been expected, too, with performance improvements in a reproducing head. It is required to increase the track density of a magnetic recording medium in order to increase the recording density among the performances of a recording head. In order to achieve this, a recording head of a narrow track structure is required to be implemented, wherein the width on the air bearing surface between a bottom pole and a top pole sandwiching a write gap is reduced to the order of some microns to submicron. Semiconductor process techniques are employed to achieve the narrow track structure.
Another factor determining the recording head performance is the throat height (TH). The throat height is the length (height) of the pole portion between the air bearing surface and the edge of the insulating layer electrically isolating the thin-film coil for generating magnetic flux. A reduction in throat height is desired in order to improve the recording head performance. The throat height is controlled as well by an amount of lapping when the air bearing surface is processed.
Furthermore, a reduction in length of the portion of the bottom and top poles sandwiching the thin-film coil (called magnetic path length in the following description) is proposed in order to improve the recording head performance.
As thus described, it is important to fabricate a recording head and reproducing head appropriately balanced so as to improve performances of a thin-film magnetic head.
Referring to the accompanying drawings, the configuration of the thin-film coil that determines the magnetic path length and a method of fabricating the coil will now be described.
FIG. 1 to FIG. 8 illustrate main parts of a method of manufacturing a composite thin-film magnetic head having an MR element as an example of a typical thin-film magnetic head of related art. FIG. 1 to FIG. 8 are cross sections of the main parts of intermediate products taken along the plane orthogonal to the air bearing surface. The example shown is a composite thin-film magnetic head made of an induction-type thin-film magnetic head for recording stacked on a magnetoresistive effect type composite thin-film magnetic head for reproduction.
As shown in FIG. 1, an insulating layer 102 made of alumina (Al.sub.2 O.sub.3), for example, of about 5 to 10 .mu.m in thickness is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al.sub.2 O.sub.3 --TiC), for example. On the insulating layer 102 a bottom shield layer 103 of 3 to 4 .mu.m in thickness is formed which makes up a magnetic shield layer for protecting an MR element (an MR film 105 described below) of a reproducing head from an external magnetic field. Next, on the bottom shield layer 103 alumina of 100 to 200 nm in thickness, for example, is deposited through sputtering to form a shield gap film 104. On the shield gap film 104 the MR film 105 of tens of nanometers in thickness for making up the MR element of the reproducing head is formed and a desired shape is obtained through high-precision photolithography. Next, a shield gap film 106 is formed on the shield gap film 104 and the MR film 105 is buried in the shield gap films 104 and 106. Next, on the shield gap film 106 a magnetic layer 107 of Permalloy (NiFe) of 3 to 4 .mu.m in thickness is formed. The magnetic layer 107 not only functions as a top shield layer for magnetically shielding the GMR element of the reproducing head together with the bottom shield layer 103 described above but also functions as a bottom pole of the recording head. For convenience of description, the magnetic layer 107 is simply called bottom pole 107 in the following description, attention being focused on the fact that the magnetic layer 107 is one of the magnetic layers forming the recording head.
Next, as shown in FIG. 2, on the bottom pole 107, a recording gap layer 109 made of a nonmagnetic material such as alumina having a thickness of about 200 nm is formed. A photoresist 110 for determining the reference position of the throat height is formed on the recording gap layer 109 except the part to make up the pole. A thin seed layer 111 made of copper (Cu), for example, of the order of 100 nm in thickness is formed through sputtering over the whole surface. The seed layer 111 is to be a seed of forming a thin-film coil by electroplating. Next, a thick photoresist 112 of 3 to 4 .mu.m in thickness is formed on the seed layer 111. A helical opening 113 that reaches the seed layer 111 is formed in the photoresist 112 by photolithography. The depth of the opening 113 is equal to the thickness of the photoresist 112 and the width is about 2 .mu.m. The width of the helical photoresist pattern formed by the opening 113 is about 2 .mu.m as well.
Next, as shown in FIG. 3, copper electroplating is performed with copper sulfate to form a coil element 114 making up a first layer of the thin-film coil in the opening 113 of the photoresist 112. The thickness of the coil element 114 is preferably thinner than the depth of the opening 113 and may be 2 to 3 .mu.m.
As shown in FIG. 4, the photoresist 112 is removed. As shown in FIG. 5, milling with argon ion beams IB (ion milling) is performed to remove the seed layer 111 and separate the turns of the coil element 114 from one another so as to form a coil 114a of the first layer. The ion milling is performed at an angle of 5 to 10 degrees with respect to the normal to the substrate in order to prevent the seed layer 111 at the bottom of the coil element 114 between the turns from projecting outward the thin-film coil and remaining. If ion milling is performed at an angle nearly orthogonal to the substrate in such a manner, the material of the seed layer 111 may scatter with the impact of ion beams and redeposit. As a result, complete separation of the turns of the coil element 114 may be made impossible. It is therefore required to allow relatively wide spacing among the turns of the coil element 114, which will be described later.
Next, as shown in FIG. 6, a photoresist 115 is formed to cover the coil 114a of the first layer and the photoresist 110. Heat treatment at a temperature of 250.degree. C., for example, is performed to flatten the coil 114a and to determine the apex angle described below and so on. Next, as shown in FIG. 6, a coil 117a of a second layer including a seed layer 116 is formed on the photoresist 115 through the steps similar to those shown in FIG. 2 to FIG. 5. A photoresist 118 is further formed. As shown in FIG. 7, the recording gap layer 109 is selectively etched in a portion behind the coils 114a and 117a (the right side of FIG. 7) to form a magnetic path. A top pole 119 of Permalloy, for example, of 3 to 5 .mu.m is then formed. The top pole 119 comes to contact with the bottom pole 107 and is magnetically coupled to the bottom pole 107 in a portion behind the coils 114a and 117a.
As shown in FIG. 8, the recording gap layer 109 and the bottom pole 107 are etched by about 0.5 .mu.m with a pole portion 119a of the top pole 119 as a mask so as to form a trim structure described below. As shown in FIG. 7, an overcoat layer 120 of alumina, for example, is formed to cover the whole surface. FIG. 8 is a cross section of the layered structure of FIG. 7 taken along the plane passing through the MR layer 105 and parallel to an air bearing surface 122. In FIG. 8 the shield gap layers 104 and 106 for electrically isolating the MR layer 105 from the other layers and magnetically shielding the MR layer 105 are separately shown. Lead layers 121a and 121b made of conductive layers for providing electrical connection to the MR layer 105 are shown as well. The overcoat layer 120 is omitted in FIG. 8. Finally, lapping of a slider is performed and the air bearing surface 122 of the recording head and the reproducing head is formed as shown in FIG. 7. The thin-film magnetic head is thus completed.
In FIG. 7, TH represents the throat height and MR-H represents the MR height. Besides the throat height and the MR height, the apex angle indicated with .theta. in FIG. 7 determines the performance of the thin-film magnetic head. The apex angle is the angle between straight line S passing through the corners of the sides of the photoresists 110, 115 and 118 closer to the air bearing surface and the upper surface of the top pole 119.
In FIG. 8, P2W indicates the magnetic pole width. As shown, the structure is called trim structure wherein the sidewalls of the pole portion 119a of the top pole 119, the recording gap layer 109, and a portion 107a of the bottom pole 107 are vertically formed in a self-aligned manner. The trim structure suppresses an increase in the effective track width due to expansion of the magnetic flux generated during writing of the narrow track.
In practical manufacturing of the thin-film magnetic head, a wafer on which a plurality of structures described above are formed are divided into a plurality of bars on which a plurality of thin-film magnetic heads are arranged. A side of each bar is lapped to obtain the air bearing surface 122 (FIG. 7). During the step of forming the air bearing surface 122, the MR film 105 is lapped as well and composite thin-film magnetic heads each having desired throat and MR heights are obtained. Although the practical thin-film magnetic head has a contact pad for providing electrical connection to the thin-film coils 114a and 117a and the MR film 105, the contact pad is omitted in the drawings described so far.
The composite thin-film magnetic head formed as described above has the following problems with respect to micromachining of the recording head in particular.
In general, a reduction in magnetic path length LM improves characteristics of an induction thin-film magnetic head such as flux rise time, nonlinear transition shift (NLTS) and overwrite. As shown in FIG. 7, magnetic path length LM is the length of part of the bottom pole 107 and the top pole 119 that surrounds the coil 114a of the first layer and the coil 117a of the second layer (that is, the length between the air bearing surface and the opening formed in the recording gap layer 109. The flux rise time is the lapse of time between the point when a current is fed to the thin-film coil made up of the coil 114a and the coil 117a and the point when the flux density in the magnetic circuit made up of the bottom pole 107 and the top pole 119 reaches a specific level. The high frequency characteristic during recording depends on the flux rise time. The nonlinear transition shift is a phenomenon detected during data recording wherein the magnetic flux from the magnetic domain in which immediately previous recording is made produces an interaction with the flux of the recording head and the position of transition (the portion where the magnetization direction is reversed) where another recording is to be made is thereby shifted. The nonlinear transition shift determines not only accuracy of data recording positions but also the surface recording density when data is recorded.
In order to reduce magnetic path length LM, it is required to reduce coil bundle width LC of the coil 114a of the first layer and the coil 117a of the second layer surrounded by the bottom pole 107 and the top pole 119. To reduce coil bundle width LC, it is required to reduce the width of each turn of the coil 114a and the coil 117a (simply called thin-film coil in the following description except where stated otherwise) or to reduce the space between the turns. However, it is difficult to reduce the width of each turn of the thin-film coil and the space between the turns of the thin-film magnetic head of related art described above because of the following reasons.
First, there is a limitation in reducing the width of each turn since the electric resistance of the thin-film coil is required to be reduced. Even if copper whose conductivity is high is used to reduce the resistance of the thin-film coil, the height of at least 2 to 3 .mu.m is required to maintain the cross-sectional area of the thin-film coil. Therefore, the width of the turn of the thin-film coil as narrow as 1.5 .mu.m or below may affect the structural stability. It is thus difficult to further reduce the width of each turn of the thin-film coil.
It is difficult to reduce the space between the turns of the thin-film coil due to the following two reasons.
The first reason is as follows. The thin-film coil of related art described above is formed through electroplating as described with reference to FIG. 3. The thin seed layer 111 is formed beforehand so as to deposit copper evenly throughout the wafer in the opening 113 formed in the photoresist 112. Consequently, the seed layer 111 in the opening 113 is required to be selectively removed to separate the coils after the formation of the coil element 114 in the opening 113 through electroplating. As described with reference to FIG. 5, the seed layer 111 is removed by ion milling using argon, for example, with the coil element 114 as a mask. Basically, ion milling is preferably performed at an angle nearly orthogonal to the substrate surface. However, etched copper is redeposited and the turns of the thin-film coil are shorted and insufficient insulation may result. In order to avoid this, ion milling is required to be performed at an angle of a certain degree with respect to the normal to the substrate. In general, redeposition of etchant is almost prevented if ion milling is performed at an angle as large as 40 to 45 degrees with respect to the normal to the substrate. However, when ion milling is performed at such a large angle, sufficient ion beams are not applied to the part obstructed by the coil element 114 and a large part of the seed layer 111 in the opening 113 remains. Therefore, ion milling is performed at an angle of 5 to 10 degrees in general as described with reference to FIG. 5. However, if a further reduction in the space between the turns of the thin-film coil is intended, an application of sufficient ion beams is not achieved to the part obstructed by the coil element 114 even though the ion milling angle is as small as 5 to 10 degrees. As a result, the seed layer 111 partly remains and causes a short circuit of the turns. If the ion milling angle is 5 to 10 degrees or below as described above, a short circuit of the coils occurs as well due to redeposition of etchant. It is therefore difficult to reduce the space between the turns of the thin-film coil to 2 to 3 .mu.m or below.
The second reason is as follows. In order to reduce the space between the turns of the coil element 114 to 1 .mu.m or below, the helical pattern width (wall thickness) of the photoresist 112 is required to be narrow (thin). In addition, the depth of the opening 113, that is, the thickness of the photoresist 112 is required to be 3 to 4 .mu.m so as to make the height of the thin-film coil 2 to 3 .mu.m as described above. However, an electrolyte such as copper sulfate is required to be stirred in order to obtain an even thickness of the film when the thin-film coil is formed through electroplating as described with reference to FIG. 3. Consequently, if the helical pattern width (wall thickness) of the photoresist 112 is made too thin in order to reduce the space between the turns of the coil element 114, the thin wall collapses due to stirring of the electrolyte and correct formation of the thin-film coil is made impossible. It is therefore difficult to reduce the space between the turns of the thin-film coil.
It is difficult to make the width of each turn of the thin-film coil and the space between the turns narrower than those of the related art magnetic head because of the reasons described so far. Consequently, a reduction in coil bundle width LC is difficult.
In order to improve the NLTS characteristic of the recording head mentioned above, the number of turns of the thin-film coil may be increased. However, the number of layers of the thin-film coil layers is required to be increased to four to five in order to increase the number of turns without increasing coil bundle width LC nor without reducing the width of each turn of the thin-film coil and the space between the turns. However, if the number of layers of the thin-film coil layers is increased, apex angle .theta. described above is made large and it is impossible to achieve the narrow track width (narrowing magnetic pole width P2W of FIG. 8). In order to maintain apex angle .theta. within a specific range, the number of thin-film coil layers is required to be three or below or preferably two or below. However, it is impossible to increase the number of turns and it is therefore difficult to improve the NLTS characteristic.
The publications relating to the thin-film magnetic head include: Japanese Patent Application Laid-open Sho 63-204504 (1988), Japanese Patent Publication Sho 55-41012 (1980) (U.S. Pat. No. 4,416,056), Japanese Patent Application Laid-open Hei 02-27508 (1990), Japanese Patent Application Laid-open Hei 02-302920 (1990) (U.S. Pat. No. 5,065,270), Japanese Patent Application Laid-open Hei 05-242430 (1993), Japanese Patent Application Laid-open Hei 02-14417 (1990), Japanese Patent Application Laid-open Hei 05-182135 (1993).